The present invention relates to a microstructure having a catalyst supported in micropores and a method of manufacturing the same.
In the technical field of metal and semiconductor thin films, wires and dots, it is known that the movement of free electrons becomes confined at sizes smaller than some characteristic length, as a result of which singular electrical, optical and chemical phenomena become observable. Such phenomena are called “quantum mechanical size effects” or simply “quantum size effects.” Functional materials which employ such singular phenomena are under active research and development. Specifically, materials having structures smaller than several hundred nanometers in size, typically called microstructures or nanostructures, are the subject of current efforts in material development.
Methods for manufacturing such microstructures include processes in which a nanostructure is directly manufactured by semiconductor fabrication technology, including micropatterning technology such as photolithography, electron beam lithography, or x-ray lithography.
Of particular note is the considerable amount of research being conducted today on processes for manufacturing nanostructures having an ordered microstructure.
One method of forming an ordered structure in a self-regulating manner is illustrated by an anodized alumina layer (anodized layer) obtained by subjecting aluminum to anodizing treatment in an electrolytic solution. It is known that a plurality of micropores having diameters of about several nanometers to about several hundreds of nanometers are formed in a regular arrangement within the anodized layer. It is also known that when a completely ordered arrangement is obtained by the self-ordering treatment of this anodized layer, hexagonal columnar cells will be theoretically formed, each cell having a base in the shape of a regular hexagon centered on a micropore, and that the lines connecting neighboring micropores will form equilateral triangles.
For example, H. Masuda et al. (Jpn. J. Appl. Phys., Vol. 37, Part 2, No. 11A, pp. L1340-1342 (Nov. 1, 1998), FIG. 2) describes an anodized layer having micropores. In another related publication (Hyomen Gijutsu Binran [Handbook of Surface Technology], edited by The Surface Finishing Society of Japan (Nikkan Kogyo Shimbun Co., Ltd., 1998), pp. 490-553), it is described that micropores are naturally formed in an anodized layer as oxidation proceeds. Moreover, H. Masuda (“Highly ordered metal nanohole array based on anodized alumina”, Kotai Butsuri (Solid State Physics], Vol. 31, No. 5, pp. 493-499 (1996)) has proposed the formation of a gold dot array on a silicon substrate using a porous anodized layer as the mask.
A plurality of micropores take on a honeycomb-like structure in which the pores are formed parallel in a direction substantially vertical to the substrate surface, and at substantially equal intervals. This point is deemed to be the most distinctive characteristic of anodized layers in terms of material. Another remarkable feature of anodized layers, thought to be absent in other materials, is the ability to relatively freely control the pore diameter, pore spacing and pore depth (see Masuda, 1996).
Known examples of applications for anodized layers include various types of devices, such as nanodevices for supporting catalysts, optical functional devices, magnetic devices, and luminescent devices. For example, JP 2000-31462 A mentions a number of applications, including magnetic devices in which the micropores are filled with the magnetic metal cobalt or nickel, luminescent devices in which the micropores are filled with the luminescent material ZnO, and biosensors in which the micropores are filled with enzymes/antibodies.